U.S. Pat. No. 4,946,107 describes a conventional fuel injection valve in which a fuel filter at the inflow end of the fuel injection valve is inserted into the fuel inlet fitting. In this, a projection provided internally on the inflow end of the fuel inlet fitting snaps into a groove provided on the enveloping surface of the fuel filter in order to secure the fuel filter on the fuel inlet fitting. The fuel inlet fitting has a stepped bore whose step offers a stop for the fuel filter being inserted. In addition, a retaining collar which projects radially beyond the inflow end of the fuel inlet fitting and also comes to a stop against the inflow-end face of the fuel inlet fitting, is provided. This prevents the fuel filter from penetrating too far into the fuel inlet fitting. The conventional fuel injection valve has several disadvantages. The stepped bore provided in the fuel inlet fitting and the configuration of the projection which snaps into the groove of the fuel filter require a material-removing machining method, so that there is a not inconsiderable production outlay in order to prepare the fuel inlet fitting to receive the fuel filter. On the other hand, configuring the retaining collar on the fuel filter requires a relatively complexly shaped injection-molded element for production of the fuel filter using a plastic injection-molding method.
It is particularly disadvantageous, however, that a completely satisfactory sealing effect is not present between the fuel inlet fitting and the fuel filter. Sealing between the fuel filter and the inflow end of the fuel inlet fitting is impaired in particular by the fact that the plastic material of the fuel filter can swell or shrink as the result of a chemical or physical interaction with the fuel to be filtered, which can considerably impair the fit between the fuel inlet fitting and the fuel filter.
Other fuel injection valves having fuel filters inserted into the inflow end of the fuel inlet fitting are described in German Patent Application No. 43 25 842 and U.S. Pat. No. 5,356,079. These conventional fuel injection valves differ substantially from the fuel injection valve described in U.S. Pat. No. 4,946,107 in that the snap connection between the fuel inlet fitting and the fuel filter is provided not internally but externally on the fuel inlet fitting. The disadvantages described above--in particular the fact that the snap elements to be provided on the fuel inlet fitting must be produced using a material-removing production method, that the fuel filter is of relatively complex shape because of the retaining collar, and that because of the swelling or shrinkage behavior of the plastic material of the fuel filter, sealing between the fuel filter and the fuel inlet fitting is unsatisfactory--also exist for the fuel injection valves evident from the two last-named documents.
German Patent Application 40 03 228 discloses a fuel injection valve in which the fuel filter is pressed into the fuel inlet fitting. This fuel filter is equipped at the periphery with, for example, a brass ring that constitutes a pairing with the wall of the fuel inlet fitting when the fuel filter is pressed in. When the fuel filter equipped with a brass ring is pressed in, however, there exists a risk of the occurrence of abrasion and chips, which may be detached because of the compressive stress between the fuel filter and fuel inlet fitting and cause contamination in the fuel injection valve. Here again, unsatisfactory sealing can occur between the brass ring of the fuel filter and the fuel inlet fitting if the fuel inlet fitting is made of a different metal which has a coefficient of thermal expansion different from the brass of the attachment ring of the fuel filter, so that the risk exists that heating of the fuel injection valve due to engine heat will create a gap which does not seal. A further disadvantage is that because of the relatively large pressing forces to be applied when the brass ring of the fuel filter is pressed into the fuel inlet fitting, it is practically impossible to remove the fuel filter from the fuel inlet fitting thereafter.